1. Field of the Invention
The present invention relates to a liquid crystal display device comprising drive circuitry including an active element, and a pixel driving element, the drive circuitry and the pixel driving element being formed on the same substrate. More particularly, the present invention relates to a liquid crystal display device in which a common transition electrode is disposed via an insulating layer in a drive circuit region in which drive circuitry is provided.
2. Description of the Related Art
A liquid crystal display device is known as a device for displaying images. The liquid crystal display device displays images by controlling a voltage applied across liquid crystal material interposed between a base substrate and a counter substrate.
One type of a liquid crystal display device is an active matrix type liquid crystal display device. An active matrix type liquid crystal display device includes a thin film transistor (TFT) preferably used as a switching element for driving a pixel having steep on-off characteristics. Therefore, an active matrix type liquid crystal display device has high-speed response and can have a large number of pixels, resulting in a large-size and high-definition display.
Hereinafter, an active matrix type liquid crystal display device in a driver monolithic form will be described. The phrase xe2x80x9cdriver monolithic formsxe2x80x9d means that a driver and pixel electrodes controlled by the driver are provided on the same substrate. Images are displayed on the liquid crystal display device by the driver controlling pixel electrodes.
FIG. 7 is a top view of a base substrate 550 of an active matrix type liquid crystal display device 500 in a conventional driver monolithic form.
A display region 501 is provided in a middle portion of a surface of the base substrate 550 facing a counter substrate (not shown in FIG. 7). Referring to FIG. 7, a scanning driver 505 and a data driver 506 are provided around the display region 501. A plurality of common transition electrodes 508 are provided at a further peripheral region of the base substrate 550 than the scanning driver 505 and the data driver 506. A signal input terminal 507 provided on a portion of the peripheral region supplies power to a counter electrode (not shown) on the counter substrate through the common transition electrodes 508. The common transition electrodes 508 are electrically connected to a peripheral portion of the counter electrode via conductive paste.
FIG. 8 is an enlarged diagram of a portion A (FIG. 7) of the base substrate 550 of the liquid crystal display device 500. Referring to FIG. 8, in the display region 501, a plurality of scanning signal lines 502 and a plurality of data signal lines 503 are provided in such a manner as to intersect. The pixel driving elements (e.g., TFTs) and pixel electrodes 504 are arranged in a matrix, each pair of which are provided in the vicinity of an intersection. The gate electrodes of the TFTs provided on the same row are connected to a common scanning signal line 502. The scanning signal line 502 on each row is connected to the scanning driver 505. The drain (or source) electrodes of the TFTs provided on the same column are connected to a common data signal line 503. The source (or drain) electrodes of the TFTs are connected to the pixel electrode 504. The data signal line 503 on each column is connected to the data driver 506.
The scanning driver 505 progressively scans the scanning signal lines 502 (a scanning signal line 502 is provided in each row). The data driver 506 is controlled so that image data is progressively applied from the data signal lines 503 to the respective pixel electrodes 504 via the TFTs, thereby displaying images in the display region 501.
Typically, the counter electrode provided on the counter substrate is a transparent electrode made of ITO (indium tin oxide) or the like. The electric resistance of the counter electrode is relatively large. Particularly in a large-sized liquid crystal display device, brightness gradation, irregular display, or the like may occur due to a delay of a polarity inversion signal caused by distributed resistance in the counter electrode and liquid crystal capacitance. To avoid this, for example, the common transition electrodes 508 are provided at a plurality of portions of the base substrate 550. In the case of a liquid crystal display device using TAB (tape automated bonding), the pitch of the TAB is narrowed so that a common transition electrode is provided between the TABs. However, in a typical liquid crystal display device in a driver monolithic form, a plurality of the common transition electrodes 508 are provided at a further peripheral region of the base substrate 550 than the scanning driver 505 and the data driver 506.
Recently, the miniaturization of devices is in increasing demand. An even smaller size liquid crystal display device is desired. In a liquid crystal display device, the area of the display region 501 viewed by a user should be increased as much as possible while the surrounding region of the display region 501 which has substantially no contribution to display is reduced as much as possible.
Needless to say, the same applies to the above-described active matrix type liquid crystal display device 500 in the driver monolithic form. A portion having substantially no contribution to display, in which the drive circuitry including the scanning driver 505 and the data driver 506 and the common transition electrodes 508 are provided, can be reduced with respect to the display region 501.
However, when a plurality of the common transition electrodes 508 are provided outside the scanning driver 505 and the data driver 506 in the liquid crystal display device 500, the width of the peripheral portion of a liquid crystal display device, which has substantially no contribution to display, is significantly increased.
Further, when conductive paste is applied to the common transition electrodes 508 using a printing process, static electrical charge tends to occur. Such static electrical charge is likely to cause fluctuation of the threshold of an active element in a circuit in the vicinity of the common transition electrode 508. Particularly when the threshold fluctuation occurs in a switching element for sampling in the data driver 506 within the active matrix type liquid crystal display device 500 in the driver monolithic form, a sampling level to image display data is varied for each data signal line 503, so that display quality is significantly reduced.
Further, when conductive paste is applied to the common transition electrodes 508, excessive charge transfer occurs due to the potential (or charge quantity) difference between a glass substrate and an application device. This charge transfer is likely to cause a change in characteristics, such as threshold fluctuation, of an active element within a circuit in the vicinity of the common transition electrode 508.
The data driver 506 includes an active element other than the switching element for sampling. For example, a logic circuit such as a shift register circuit within the data driver 506 includes an active element. The logic circuit is only required to transfer and/or identify a digital signal expressed by 0 or 1. Therefore, a certain degree of a threshold fluctuation of an active element in the logic circuit does not have a substantial influence on display quality.
The switching element for sampling needs to charge each data signal line 503 with analog image display data in a certain limited time, e.g., about 160 ns for a QVGA display format. When threshold fluctuation occurs in the switching element for sampling, the sampling level to the image display data is varied for each data signal line 503 due to a difference in a charge capability between each element. Therefore, a display quality is significantly reduced.
According to one aspect of the present invention, a liquid crystal display device comprises a base substrate including a display region, and a drive circuitry region provided in a surrounding region of the display region, a liquid crystal layer, and a counter substrate facing the base substrate via the liquid crystal layer. A pixel electrode and a pixel driving element for driving the pixel electrode are provided in the display region. A driving circuitry section for controlling the pixel electrode and the pixel driving element is provided in the drive circuitry region. An insulating layer is provided to cover at least one portion of the drive circuitry region. A common transition electrode is provided in the insulating layer. The common transition electrode is electrically connected to a counter electrode provided on the counter substrate.
The drive circuitry region includes data drivers for converting serial data to parallel data so as to drive data signal lines, conductor sections between the data drivers, scanning drivers for driving scanning signal lines, and conductor sections between the scanning drivers. The data driver may include a shift register, a buffer circuit section, a sample holding circuit section (including a latch circuit section for latching a digital signal), and a DAC circuit section for converting a digital signal to an analog signal. The scanning driver may include a shift register and a buffer circuit section.
In this configuration, the common transition electrode is provided via the insulating film in the drive circuitry region. Therefore, it is possible to prevent a threshold fluctuation of an active element in the drive circuitry due to static electric charge generated in the common transition electrode. A reduction in liquid crystal display quality can also be prevented. Further, the common transition electrode can be efficiently provided in the drive circuitry region, thereby reducing the surrounding region of a display region of the liquid crystal display device which has substantially no contribution to display. Therefore, the liquid crystal device can be miniaturized.
In one embodiment of this invention, the drive circuitry section includes a plurality of types of active elements. The common transition electrode is provided on a portion of the insulating layer corresponding to the drive circuitry region other than a portion of the drive circuitry region. On the portion of the drive circuitry region, a specific type(s) of active element(s) out of the plurality of types of active elements is provided.
In one embodiment of this invention, the specific type of the active element is a switching element for sampling.
The specific type of active element may be, for example, an active element in a shift register circuit or a buffer circuit, for example.
A common transition electrode is provided via an insulating film in a drive circuitry region which does not include an active element (or a specific active element). Therefore, it is possible to prevent a threshold fluctuation of an active element due to static electric charge generated in the common transition electrode. A reduction in liquid crystal display quality can also be prevented. Further, the common transition electrode can be efficiently provided in the drive circuitry region, thereby reducing the surrounding region of a display region of the liquid crystal display device which has substantially no contribution to display. Therefore, the liquid crystal display device can be miniaturized.
The above-described drive circuitry region for display includes a scanning driver for driving a scanning signal line and a data driver for driving a data signal line. In the data driver, a sample holding circuit as well as a shift register circuit are provided. A threshold fluctuation of an active element other than the switching element for sampling included in the sample holding circuit of the data driver does not have a substantial influence on display quality. Therefore, when the common transition electrode is provided via the insulating layer on a portion of the drive circuitry region which does not include the switching element for sampling, i.e., the drive circuitry region other than the sample holding circuit (e.g., a shift register circuit), threshold fluctuation of the switching element for sampling can be suppressed, resulting in stable display quality. The surrounding region of a display region of the liquid crystal display device which has substantially no contribution to display can be reduced, thereby making it possible to miniaturize the liquid crystal display device.
In one embodiment of this invention, a plurality of drive circuitry sections and a plurality of conductors connecting the plurality of drive circuitry sections are provided in the drive circuitry region. The common transition electrode is provided on a portion of the insulating layer corresponding to a portion of the driving circuitry region. On the portion of the driving circuitry, at least one portion of the conductors is provided.
In this configuration, an array pitch in a drive circuit section of each predetermined drive circuit is reduced, thereby providing a conductor region. A common transition electrode is provided via an insulating film on the conductor region. Therefore, the common transition electrode is provided via the insulating film in a portion of the drive circuitry region which does not include an active element.
In one embodiment of this invention, the drive circuitry section includes a scanning driver for driving a scanning signal line and a data driver for driving a data signal line. At least one of the scanning driver and the data driver includes a shift register circuit having at least one stage. An array pitch of the stage in the shift register circuit is less than an array pitch of the pixel electrode connected to the scanning signal line and/or the data signal line.
With this configuration, an array pitch in a drive circuit section is reduced, thereby easily providing a conductor region.
In one embodiment of this invention, the common transition electrode is shaped so as to be a rectangular, a annular, or a stripe.
The drive circuitry region includes a scanning driver for driving a scanning signal line and a data driver for driving a data signal line. The scanning driver is provided opposite vertical ends of a display panel while the data driver is provided on opposite horizontal ends of the display panel, for example. In this case, the stripe-shaped common transition electrode provided throughout the drive circuitry region includes a stripe-shaped portion thereof provided across a scanning driver region at the left side of the display panel, a stripe-shaped portion thereof provided across a scanning driver region at the right side of the display panel, a stripe-shaped portion thereof provided across a data driver region at the top side of the display panel, and a stripe-shaped portion thereof provided across a data driver region at the bottom side of the display panel. The present invention is not limited to this. The stripe-shaped common transition electrode may be any one of the above-described portions, or may be contiguous and extends annularly throughout the peripheral portion of the display panel.
With this configuration, the stripe-shaped common transition electrode is provided throughout the drive circuitry region, thereby causing additive capacitance on the drive circuitry to be uniform. Therefore, a more stable display quality can be achieved.
Thus, the invention described herein makes possible the advantages of providing a liquid crystal display device in which a surrounding region of a display region which has substantially no contribution to display is decreased without a reduction in display quality so that the liquid crystal display device can be miniaturized.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.